Gammaray emission from AGN Qinghuan Luo School of

Gamma-ray emission from AGN Qinghuan Luo School of Physics, University of Sydney ICRR 17/9/2001

Blazars • EGRET sources: Most of them are AGN Third EGRET Catalog • Diffuse -ray background: - Unresolved blazars or - Exotic processes e. g. annihilation lines from supersymmetric particle dark matter or unstable particle relics? ICRR 17/9/2001 (Hartman et al 1999)

Mk 421, Mk 501 ICRR 17/9/2001

3 C 273, 3 C 279 ICRR 17/9/2001

Rapid variations Mk 501 ICRR 17/9/2001

Overview • Blazars (BL Lac, FSQ): Relativistic jets directed at a small angle to the line of sight. • Intraday variability (IDV): small scales; large . • Relativistic jets, contents, acceleration/deceleration. • Emission mechanisms: SSC vs ERC? • Emission from decelerating/accelerating jets? ICRR 17/9/2001

High energy spectra of blazars • At least two components: IR-UV (perhaps up to X-rays) and above hard X-rays • High energy range is power-law, =-∂ln. L /∂ln. E≈0. 6 -1. 6 for EGRET blazars • Te. V -rays; No evidence for -ray absorption due to pair production ICRR 17/9/2001

Te. V -rays from Mk 421, Mk 501 : Mk 421 (Krennrich et al 1999) ICRR 17/9/2001

Escape of Te. V -rays A large is needed to explain IDV in -ray emission from Mk 501 • Absorption of Te. V -rays via + e++e-. Photon number density nph≈F d 2/(c 3 t 2 var. D 4) (Protheroe 1998) • The maximum photon energy: ph~D maxmec 2 in the KN regime; ph ~15 Te. V requires D ~30 for =106. ICRR 17/9/2001

Te. V flares -Intraday variability (possibly ~ hrs) requires relativistic beaming! ICRR 17/9/2001 Mrk 501

Radio IDV PKS 0405 -385 (Kedziora-Chudczer et al. 1997) ICRR 17/9/2001

The brightness temperature problem -VLBI measurement: • Space-based VLBI survey: the highest Tb=1. 8 1012 K (0133+476) (Lister et al 2001; Tingay et al 2001). • The intrinsic brightness temperature: T’b=Tb(1+z)/D, D=[ ( bcos )]-1 -Variability brightness temperature: Tvar= S d 2/ 2 2 t 2 var In the jet frame T’var~Tvar/D 3 e. g. for PKS 0405 -385, Tvar= 1021 K! (Kedziora-Chudczer et al. 1997) ICRR 17/9/2001

Constraints on Tb • Synchrotron self-absorption: Tb≤ mec 2 /k. B • Inverse Compton scattering (Kellermann & Pauliny-Toth 1969) • Equipartition (Readhead 1994) • Induced scattering: -Induced Compton scattering (k. Tb/mec 2) T≤ 1 (e. g. Coppi, Blandford, Rees 1993; Sincell & Krolik 1994) -Induced Raman scattering and possibly other processes -Coherent processes is not favoured ICRR 17/9/2001

Interpretation of radio IDV • Various models - Extrinsic: Interstellar scintillation - Intrinsic: Coherent emission; Geometric effects (Spada et al 1998) Synchrotron radiation by protons (Kardashev 2000) Non-stationary models (Slysh 1992) • Relativistic bulk beaming with >10 needed? IDV may be due to both intrinsic effects and scintillation. ICRR 17/9/2001

Relativistic bulk motions • Rapid variability, high brightness temperature require relativistic bulk motion with a higher . • Continuous jets or blobs? • Observations of -ray flares, IDV appear to suggest the source region being close to the central region. • Both acceleration and deceleration of the jet can occur in the central region. • VLBI observations: ≤ 10. The limit of VLBI or acceleration mechanisms or radiation drag (e. g. Phinney 1987)? ICRR 17/9/2001

Superluminal motions - Measured obs gives only the minimum . -D from beaming models: Sobs=S 0 Dp (e. g. Kollgaard et al 1996) RBLs E=log(Pc/Pex) ICRR 17/9/2001

Formation of jets • Acceleration mechanisms: no widely accepted model. - The unipolar model: Blandford & Znajek (1977), Macdonald & Thorne (1982) - “Twin exhaust’’ model: Blandford & Rees (1974) - Radiation acc. : O’Dell (1981) - Acc. by tangled magnetic fields: Heinz & Begelman (2000) • Radiation drag: - Radiation fields from the disk and jet’s surroundings decelerate the jet Phinney (1982, 1987): ~ eq < 10. Sikora et al. (1996) ICRR 17/9/2001

Emission mechanisms: SSC vs ERC • Synchrotron self-Compton (SSC): (e. g. Konigl 1981; Marscher & Gear 1985; Ghisellini & Maraschi 1989) Synchrotron photons are both produced and Comptonized by the same Population of electrons. • External radiation Compton (ERC): The seed photons are from external sources such as disks, BR, turi, etc. (e. g. Begelman & Sikora 1987; Melia & Konigl 1989; Dermer et al. 1992) • Both SSC and ERC operate ICRR 17/9/2001

ERC Photon energy: s~2 2 2 (Thomson scattering) s~ mec 2 (KN scattering) Luminosity: LIC=(4/ 2)∫ Ajdr d. Ee/dt ne ICRR 17/9/2001

Radiation drag by external photon fields ICRR 17/9/2001

Compton drag Lab frame Incoming photons e+ e- Incoming photons ICRR 17/9/2001 e- e+ Jet frame

Compton drag (cont’d) ICRR 17/9/2001

The KN effect ICRR 17/9/2001

Equilibrium bulk • < eq: radiation forces accelerate a jet • > eq: radiation forces decelerate a jet • When acceleration is dominant, is determined by acceleration ICRR 17/9/2001

Photon fields from a disk ICRR 17/9/2001

Electron-proton jets ICRR 17/9/2001

Extended disks • Drag due to radiation fields from an extended disk - A plasma blob at z=100 Rg, 102 Rg and 3 103 Rg with =100. Pairs have a power-law, isotropic distribution in the jet frame. -An extended disk reprocesses radiation from the inner disk. - KN scattering important only for >100 -Terminal depends on the initial distance and jet content ICRR 17/9/2001

Dust torus • Drag due to radiation fields from disk + torus - Blazars with a dusty molecular torus? • The unified scheme, e. g. Barthel (1989) • -ray models for blazars (e. g Protheroe 1996) • Strong correlation between gamma-ray and near-IR luminosities for a sample of blazars (Xie et al. 1997) - Pier & Krolik (1992) model • Deceleration region extended ICRR 17/9/2001

Compton drag (cont’d) • Acceleration fast enough in < 0. 2 pc • Pair plasma in the blob relativistic • The terminal f < 20 • Acceleration occurs over a larger range f > 20 possible (determined by the acc. mechanism) ICRR 17/9/2001

Terminal Lorentz factor Bulk Lorentz factor ICRR 17/9/2001

Emission from dragged jets ICRR 17/9/2001 (e. g. Eldar & Levinson 2000)

SED ICRR 17/9/2001 (Wagner 1999)

LIC vs Lk 0=20, 50, 100 Ld=1046 erg s-1 Lj=1046 erg s-1 Z 0=103 Rg < >=5. LIC is the received power from IC: LIC=(4/ 2)∫ Ajdr d. Ee/dt ne ICRR 17/9/2001 =Lk/LB Lj=Lk+LB=1046 erg s-1.

Poynting flux dominated jets? • Equapartition but a small Lj<1046 erg s-1 • Or Lj =1046 erg s-1 but LB>Lk ICRR 17/9/2001

Equipartition Lj=Lk+LB Lsyn ne. B’ 2 Lj Lsyn/( B’)2 LB ( B’)2 (e. g. Ghisellini 1999) ICRR 17/9/2001

Multifrequency observations (Wagner 1999) ICRR 17/9/2001

Radio emission - Photosphere: the radius self-ab<1 - Doppler boosted Tb decreases - Frequency dependence of Tb - Tb changes with t ? ICRR 17/9/2001 decreases

Summary • Compton drag important and should be taken into account in modeling of blazars. • Radiation drag limit to the bulk in the central region up to 0. 1 -0. 2 pc (for Rg=1. 5 1013 cm). • The terminal is not well defined; It depends on acc. mechanisms, jet content (protons, cold electrons). A very large is not favoured. • Emission from the drag constrains jet models; multifrequency obs of IDV provide a test. • For radio IDV, when the emission region is decelerating, change in change frequency dependence of Tb. ICRR 17/9/2001